1. Field of the Invention
The present invention relates to a display apparatus to obtain a seamlessly synthesized image from images displayed on a plurality of display elements.
2. Description of the Related Art
In a large-screen display apparatus, a plurality of relatively small image display elements such as liquid crystal display elements are arranged in rows and columns to form a display apparatus as a whole, thereby creating a large screen.
FIG. 8 shows a cross sectional view of a conventional large-screen display apparatus. The display apparatus is provided with a plurality of liquid crystal elements 1, 2, and an optical fiber bundle 3 which transmits images. The liquid crystal display elements 1, 2 have display screens 1a, 2a (plane B), respectively. Input end faces 3a, 3b of the optical fiber bundle 3 are connected to the display screens 1a, 2a. With such a constitution, images can be formed without boundary at the output end face (plane A) of the optical fiber bundle 3.
FIG. 9 shows an enlarged view of a joint between the display screens 1a, 2a of the liquid crystal display elements 1, 2 and the optical fiber bundle 3 of the display apparatus described above. The liquid crystal display elements 1, 2 have a glass substrate 21, a substrate (not shown in the drawing) arranged to oppose the glass substrate 21 and a liquid crystal layer 25 sandwiched therebetween. On the liquid crystal layer 25 side of the glass substrate 21, a color filter 22, a transparent electrode 23 and an alignment film 24 are superimposed in this order, and a polarizer 20 is provided on the display screens 1a, 2a side. The color filter 22 and the end face of the optical fiber bundle 3 are separated by a distance h.
Each of the optical fibers 5 used in the optical fiber bundle 3 usually has a numerical aperture (NA) of about 0.5. Therefore image information which is output from the color filter 22 of the liquid crystal display elements 1, 2 is taken into each optical fiber 5 of the optical fiber bundle 3 in an angle of about 30.degree..
Now assume typical dimensions for the components; about 300 .mu.m for the size t of each pixel of the 4-inch liquid crystal display elements 1, 2 (one set of R, G, B elements of the color filter 22 corresponds to one pixel), 250 .mu.m for diameters of the optical fiber 5 and about 1 mm for the distance h which is the sum of the thickness of the polarizer 20 and the thickness of the glass substrate 21. In this case, the number of pixels of which image information is taken into one optical fiber 5 is around five in the X direction as is shown in FIG. 9. When the depth direction (direction perpendicular to the paper) is taken into consideration, the number of pixels corresponding to one optical fiber 5 becomes around seventeen. This means that the image information carried by one optical fiber 5 is a mixture of image information from a plurality (around seventeen in this case) of pixels, which results in deterioration of the resolution of display and decreased contrast of the image displayed at the output end of the optical fiber bundle 3.
In the display apparatus described above, factors which determine the output image contrast are the distance h which is the sum of the thicknesses of the polarizer 20 and the glass substrate 21, and the numerical aperture of the optical fiber 5. Since there is a limitation in decreasing the distance h, the distance h cannot be decreased enough to obtain a sufficiently high contrast.
Thus consider an attempt to decrease the value of the numerical aperture of the optical fiber 5 thereby to decrease the number of pixels corresponding to one optical fiber 5. For example, by setting the value of numerical aperture of the optical fiber 5 to about 0.2, the number of pixels becomes around two for the X direction in FIG. 9. Therefore, when the depth direction is taken into account, the number of pixels corresponding to one optical fiber 5 can be decreased to around four. In such a case, however, because the angle of emergence of light from the output end of the optical fiber bundle 3 tends to decrease, the viewing angle decreases thereby deteriorating the visibility of the displayed image and changing the color of the displayed image.
The problem of decreasing the viewing angle may be solved by means of providing a scattering plate or the like on the output end of the optical fiber bundle 3. However, it causes white blurring to accompany the increase in the viewing angle. Another means of changing the values of the numerical aperture at the input end face and numerical aperture at the output end face within one optical fiber 5 may be conceived, but this is impossible to manufacture. Thus images of high display contrast and good quality have not been obtained in the conventional art.
Moreover, there is another problem of occurrence of moire/ fringes. Moire/ fringes occur when any two of stripes having a certain period are superimposed upon each other. The absence of moire/ fringes occurs only when the periods of the stripes are identical and there is no off-set between the two stripes. The closer the periods of the two stripes are, the more distinct the moire/ fringes become. In the conventional display apparatus, as described above, the size t of each pixel of the liquid crystal display elements 1, 2 is about 300 .mu.m, and the diameter s of the optical fiber 5 is 250 .mu.m, which is close to the size t. Therefore, clear moire/ fringes occur in the output end face of the optical fiber bundle 3. To solve this problem, the output end of the optical fiber bundle 3 is roughened, or a scattering plate or the like is provided on the output end of the optical fiber bundle 3. In such a case, however, it also causes deterioration of the resolution and white blurring of the display. The detail description of this problem can be found in Japanese Laid-open (Kokai) Publication No. 4-324490.